Braking systems, such as air brake systems, have generally been used to control movement of motor vehicles in a safe and effective manner. In particular, air brakes are commonly used on commercial vehicles such as trucks, trailers, and buses, which typically have large gross vehicle weights. The considerable inertial mass of these heavy-duty vehicles, in combination with the high speeds at which they travel, often requires a braking system which responds rapidly with substantial braking power. One system component which may be instrumental in the operation of air brake systems is the brake actuator. The brake actuator typically provides the necessary force when braking the vehicle.
Air-operated brake actuators are either piston type or diaphragm type. In the diaphragm type spring brake actuator, two air-operated diaphragm brake actuators are typically arranged in a tandem configuration, which includes an air-operated service brake actuator for applying the normal operating brakes of the vehicle, and a spring brake actuator for applying the parking or emergency brakes of the vehicle. Both the service brake actuator and the spring brake actuator include a housing having an elastomeric diaphragm dividing the interior of the housing into two distinct fluid chambers. On the other hand, the piston brake actuator operates under basically the same principles as above described, except that instead of a diaphragm, a piston with a sliding seal at the outside diameter reciprocates in a cylinder for applying the normal and/or parking brakes of the vehicles.
In a typical service brake actuator, the service brake section is divided into a pressure chamber and a push rod chamber. The pressure chamber is fluidly connected to a source of pressurized air and the push rod chamber mounts a push rod, which is coupled to the brake assembly, whereby the introduction and exhaustion of pressurized air into the pressurized chamber reciprocates the push rod into and out of the actuator to apply and release the operating brakes.
In a typical spring brake actuator, the spring brake section is divided into a pressure chamber and a spring chamber. A push rod plate is positioned in the spring chamber between the diaphragm and a strong compression spring, whose opposing end abuts the housing. In one well-known configuration, a push rod extends from the push rod plate, through the diaphragm, into the pressure chamber, and through a dividing wall separating the spring brake actuator from the service brake actuator. The end of the actuator is fluidly connected to the pressure chamber of the service brake actuator.
When applying the parking brakes, the spring brake actuator pressure is discharged from the pressure chamber and the large force compression spring pushes the push rod plate and the diaphragm toward the dividing wall between the spring brake actuator and the service brake actuator. In this position, the push rod connected to the push rod plate is pushed forward extending into the service section through the dividing center wall applying the parking or emergency brakes and thus forcing the vehicle to stop or remain parked. To release the parking brake, the pressure chamber is closed to the atmosphere and pressurized air is introduced into the pressure chamber of the spring brake actuator which expands the pressure chamber, moving the diaphragm and push rod plate toward the opposing end of the spring brake actuator housing, thereby compressing the strong compression spring.
One known problem in association with service brake actuators of this design is that the push rod plate of an actuator is known to slip, and to move. During normal weather, the push rod plate may move out of alignment with the diaphragm. During wet weather, water mixed with road oil and dirt migrates between the push rod plate and the diaphragm, and acts as a lubricant. The push rod plate can slide radially out of center position, which can restrict the actuator stroke and/or reduce the force output of the actuator. This presents a problem as the service brake will not work as efficiently as under normal conditions, which can lead to longer stopping distances, and eventual malfunction of the service brake.
Prior art designs have attempted to solve this problem and provide an improved modification to accommodate misalignment of the push rod plate in the interior surface of the diaphragm of the service brake actuator. Different designs for diaphragms exist to solve this problem. However, prior art designs are limited as they do not efficiently and cheaply keep the push rod plate aligned with the diaphragm.
Typically, diaphragms for service brake actuators are made from a layer of fabric that forms an integral structure of the diaphragm. Diaphragms in service brake actuators are generally supported at their periphery within a housing of the actuator. Upon introduction of a fluid pressure on one side of the diaphragm, the diaphragm moves a push plate or piston to actuate a braking mechanism. The diaphragm is returned to its normal position when compressed air is released exerting an opposite force on the push rod plate.
Diaphragms for brake actuators generally are cup shaped with a bottom wall or base merging into a conical sidewall. The conical sidewall terminates at a rim which is clamped between an upper and lower portion of a housing unit. A force is exerted by the diaphragm upon a push rod plate, and the diaphragm is typically in direct contact with the push rod plate. Problems occur when the push rod plate slips laterally with respect to the diaphragm, limiting the direct touching, and proper force placement, between the diaphragm and push rod plate. This can restrict the actuator stroke and/or reduce the force output of the actuator.
It is thus desirable to develop an attachment of the push rod plate to the diaphragm for a brake actuator that is easily and cheaply manufactured, and that maintains the alignment between the push rod plate and the diaphragm.